Kinetics of the Oxygen—Tungsten Reaction at High Temperatures

Abstract

The rate of reaction of molecular oxygen with tungsten was measured from 2000° to 3300°K at pressures from 0.11 to 11.5 torr. High gas‐phase mass transfer coefficients were obtained by impinging a high‐velocity gas jet on the sample. A maximum reaction rate was observed at each O₂ pressure, the temperature of maximum rate increasing with pressure. Below the temperatures of the maxima, an apparent activation energy near 23 kcal mole⁻¹ was observed. These results are well described by the empirical equations of Perkins, Price, and Crooks, except that no transition to a regime of higher activation energy at lower temperatures was observed here and the maxima were found at slightly higher rates and temperatures than previously reported. Appreciable diffusion effects were found only near the observed maxima. These data and the 10⁻⁴ torr data of Schissel and Trulson were correlated in terms of the two‐layer oxygen‐atom adsorption model for tungsten oxidation kinetics proposed by the latter authors. Kinetic constants for a slightly modified version of this model were obtained.